Valve cap for a non-return valve

ABSTRACT

A non-return valve for a hydraulic tensioning system which is used in traction mechanism drives of internal combustion engines and which manipulates a hydraulic fluid flow between a pressure chamber and a reservoir. The non-return valve has a valve body which is inserted in a housing and which is embodied as a ball and which, when the non-return valve is closed, is supported in a spring-loaded fashion against a valve seat of a through-flow cross-section. When the non-return valve is open, the valve body is assigned to a valve seat of the housing and the flow cross-section ( 19 ) of the valve seat ensures a fluid flow through the non-return valve.

FIELD OF THE INVENTION

The present invention relates to a non-return valve for a hydraulictensioning system of traction mechanism drives of an internal combustionengine. In the operating state, the non-return valve enables athroughflow of hydraulic fluid from a hydraulic fluid reservoir into ahigh-pressure chamber in an expansion phase of the tensioning system. Inthe compression phase, the non-return valve has the task of limiting orpreventing the hydraulic fluid flow. The structure of the non-returnvalve comprises a housing which is also referred to as a valve cap orholding means, in which housing in particular a valve body designed as aball is inserted, which valve body is connected under spring loading toa throughflow cross section.

BACKGROUND OF THE INVENTION

DE 40 35 823 C1 discloses a hydraulic tensioning system for tractionmechanism drives, in particular chain drives of an internal combustionengine. A tensioning piston which is pressed against the tractionmechanism is held in a longitudinally movable manner in a cylinder. Thetensioning piston and the cylinder delimit a pressure chamber forholding a hydraulic fluid. A movement of the tensioning piston in thedirection of the traction mechanism, which may also be referred to as anexpansion phase, brings about an enlargement of the pressure chamber,wherein as a result of a vacuum which is generated, a non-return valveopens, wherein hydraulic fluid can flow into the pressure chamber. Inthe compression phase, in the event of tensioning of the tractionmechanism, the tensioning piston is loaded in the opposite direction,that is to say inwards, with the pressure in the pressure chamberincreasing, as a result of which the tensioning piston moves inwards,synchronously to an activated partial amount of hydraulic fluid via aleakage gap generated between the tensioning piston and the housing.Consequently, in the compression phase, the non-return valve prevents areturn flow of the hydraulic fluid from the pressure chamber into thestorage chamber. Said known design leads to hydraulic adhesion of thevalve body, which is designed as a ball, to the valve seat of thenon-return valve.

Furthermore, a non-return valve design is known in which the valve body,which is designed as a ball, interacts with a valve seat, which isformed centrally as a bore, in the housing or the valve cap. The knownnon-return valves consistently have a design in which the valve body,effective closing at the start of the compression phase is hindered by arelatively narrow gap generated between the valve body, which isdesigned as a ball, and the housing or the valve cap, and by flowmanipulation generated behind the valve body by the valve spring.

In the case of a design of the non-return valve in which the valve caphas a central flow cross section, said valve cap is closed off at thecomplete flow cross section of the valve by the valve body, the ball,with a space being formed between the valve spring, the valve cap andthe ball, which space likewise causes hydraulic adhesion, since thehydraulic fluid cannot flow in unhindered, and is hindered on account ofthe sealing by the valve body and also by the valve body spring.

OBJECT OF THE INVENTION

The invention is based on the object of providing a functionallyimproved non-return valve with a reduced flow resistance in order toobtain an optimum inflow of the hydraulic fluid.

SUMMARY OF THE INVENTION

According to the invention, to solve said problem, a design of thehydraulic valve is provided in which, when the non-return valve is open,the valve body interacts with a valve seat of the housing, theassociated flow cross section of which ensures a fluid flow through thenon-return valve. According to the invention, the housing or the valvecap is designed such that a valve seat, which is assigned to the base ofthe housing, intentionally does not bring about a complete closure. Thenon-return valve according to the invention which is used in hydraulictensioning systems ensures, in the open position, a fast and delay-freeflow of the hydraulic fluid from the reservoir into the pressurechamber. Improved suction of the hydraulic fluid is thereby generated inthe expansion phase, which leads to optimum switching behavior of thehydraulic valve. On the other hand, the design of the hydraulic valveaccording to the invention prevents a throughflow of hydraulic fluid inthe compression phase. Furthermore, the measure according to theinvention prevents a disadvantageous hydraulic adhesion of the valvebody to the valve seat of the housing, which leads to improvedhysteresis behavior during a reversal from the expansion phase into thecompression phase.

Dependent claims 2-9 relate to further advantageous embodiments of theinvention.

According to the invention, the valve seat on the base of the housing,which is also referred to as a valve cap, is formed by a flow crosssection which does not enter into positively locking engagement with thevalve body. In this way, even in the event of abutment of the valve bodyagainst the valve seat, a substantially unhindered flow of the hydraulicfluid into the pressure chamber can take place.

The flow cross sections in the base of the valve cap or of the housingmay be of any desired geometrical shape, wherein regardless of theirdesign, complete positively locking engagement is never generatedbetween the valve body and the valve seat which forms a flow crosssection. One preferred refinement provides a non-circular flow crosssection which interacts with the valve body. Alternatively, according tothe invention, it is expedient to insert into the base of the valve capan oval, multi-cornered, for example triangular or tetragonal flow crosssection, or a polygonal flow cross section with rounded corners.

According to the invention, it is also expedient for a plurality of flowcross sections to be arranged in the flat base of the housing or of thevalve cap. Said flow cross sections are positioned such that, in an endposition of the valve body against the valve seat of the base, saidvalve body covers the throughflow cross sections of the flow crosssections partially or in regions, such that a virtually unhinderedinflow of hydraulic fluid is possible.

As a preferred example of an arrangement of a plurality of flow crosssections, three circular bores arranged close together should beprovided, the outer contour of which bores forms an equilateraltriangle. In the case of a central arrangement of said three bores, thevalve body is supported, in an end position, on a central web betweenthe bores, as a result of which the hydraulic fluid flow in theexpansion phase is virtually uninfluenced.

It is provided in a further embodiment according to the invention thatthe flow cross section be formed in a convexly shaped portion of thebase, with the radius of curvature of the base differing from the radiusof the valve body, which is designed as a ball. For this purpose, theradius of curvature of the base is advantageously greater than that ofthe valve body. Alternatively suitable for this purpose is an inverseconfiguration, with the smaller radius of curvature of the base inrelation to that of the valve body being restricted locally to a flowcross sectional region which is adjoined by a radius of curvature whichis greater than that of the valve body. As a measure for preventingdisadvantageous hydraulic adhesion, it is also expedient for the radiusof curvature of the base, which is smaller than that of the valve body,to be provided in a stepped portion, wherein at the same time the flowcross sections are not circular but rather are, for example, oval.

The non-return valve according to the invention also includes anembodiment in which the base is designed such that a contact surfaceassigned to the valve body form different curvatures with two mutuallyperpendicular section planes which comprise in each case one movementaxis of the valve body.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are illustrated in the drawingswhich are described below, wherein the invention is not restricted tosaid exemplary embodiments. In the drawings:

FIG. 1 shows a longitudinal section of the design of a hydraulictensioning system;

FIGS. 2 a to 6 c show individual part drawings of non-return valvesaccording to the invention with differently designed flow cross sectionsin the base;

FIG. 2 a shows a first exemplary embodiment of a non-return valveaccording to the invention;

FIG. 2 b shows a plan view of the non-return valve according to FIG. 2a, in which the base encompasses an oval flow cross section;

FIG. 3 a shows a second exemplary embodiment of a non-return valveaccording to the invention;

FIG. 3 b shows the plan view of the non-return valve according to FIG. 3a, with a square recess as a flow cross section;

FIG. 4 a shows a third exemplary embodiment of a non-return valveaccording to the invention;

FIG. 4 b shows the plan view of the non-return valve according to FIG. 4a, with a polygonal flow cross section;

FIG. 5 a shows a fourth exemplary embodiment of a non-return valveaccording to the invention;

FIG. 5 b shows the plan view of the non-return valve according to FIG. 5a, in which the valve cap encompasses three bores arranged closetogether as a flow cross section;

FIG. 6 a shows a fifth exemplary embodiment of a non-return valveaccording to the invention;

FIG. 6 b shows the plan view of the non-return valve according to FIG. 6a; and

FIG. 6 c shows the side view of the non-return valve according to FIG. 6b.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional illustration of a hydraulic tensioning system 1which is assigned to a traction mechanism drive and which interacts witha traction mechanism of a traction mechanism drive indirectly via atensioning roller not shown in FIG. 1. The assembly comprises a housing2 which is articulatedly connected in a positionally fixed and pivotablemanner via a fastening lug 3 a for example to a housing of the internalcombustion engine. The housing 2 forms a pot-shaped component in which acylinder 4 is inserted centrally, which cylinder 4 is designed toreceive a linearly movable piston 5. The cylinder 4 in conjunction withthe piston 5 delimit a hydraulic-fluid-filled pressure chamber 6 whichis connected via a duct 8 of the housing 2 and a throughflow crosssection 12 of the cylinder 4 to a reservoir 9 for the hydraulic fluid.Here, the reservoir 9 is delimited at the outside by the housing 2 andat the inside by the lateral surface of the cylinder 4. A pressurespring 10 which is also integrated in the cylinder 4 is supported withone spring end against a base of the housing 2 and with the other springend against a disk 11 which is positionally fixed to the piston 5. Thepressure spring 10 loads the piston 5 in the direction of a forcedirection “R” and brings about an actuating movement of the piston 5 andconsequently the exertion of a force on a tensioning roller which isconnected to the fastening lug 3 b. Said piston movement, which is alsoreferred to as an expansion movement, results in a vacuum in thepressure chamber 6, as a result of which hydraulic fluid flows into thepressure chamber 6 via the non-return valve 7 from the reservoir 9through the duct 8 of the housing 2 and the throughflow cross section 12of the cylinder 4. In the compression phase, during an inverse actuatingmovement of the piston 5 in the force direction “F”, the non-returnvalve 7 closes by virtue of a valve body 13 being supported sealingly onthe valve seat 14. Here, the piston 5 which passes into the pressurechamber 6 displaces a partial amount of the hydraulic fluid out of thepressure chamber 6 into the reservoir 9 via a leakage gap 15 generatedbetween the piston 5 and the cylinder 4.

FIGS. 2 a-6 c show variants of non-return valves designed according tothe invention, which differ in particular by having differently designedflow cross sections in the base of the housing of the non-return valve.

FIGS. 2 a and 2 b show different views of the non-return valve 16, inwhich the pot-shaped housing 17, which is also referred to as the valvecap, encompasses in the base 18 an oval flow cross section 19 whichforms the valve seat 21. On account of the oval shape of the flow crosssection 19, the latter is not fully closed by the valve body 20, whichis designed as a ball, in the end position. It is thereby possible inthe expansion phase for a partial quantity of the hydraulic fluid toflow through the non-return valve 16.

According to FIGS. 3 a, 3 b, the base 18 of the non-return valve 16 hasa square-shaped flow cross section 22, which likewise forms a valve seat23 which is not fully closed by the valve body 20 bearing against it.

FIGS. 4 a, 4 b show a polygonal flow cross section 24 in the base 18 ofthe housing 17, which likewise does not permit complete positivelylocking engagement with the valve body 20.

A further variant is shown in FIGS. 5 a, 5 b, in which the non-returnvalve 16 encompasses, as a flow cross-section 26, three identicallydimensioned bores which are formed in the base 18 in an equilateraltriangle and which, together form a valve seat 27 which can be closedoff by the valve body 20 only to a limited extent.

According to FIGS. 6 a-6 c, the non-return valve 16 encompasses ahousing 17 with a base 18 which is designed such that a contact surface31 assigned to the valve body 20 comprises two mutually perpendicularsection planes 32 a, 32 b which in each case form a movement axis of thevalve body 20 with different curvatures to one another.

LIST OF REFERENCE SYMBOLS

-   -   1 Tensioning system    -   2 Housing    -   3 a Fastening lug    -   3 b Fastening lug    -   4 Cylinder    -   5 Piston    -   6 Pressure chamber    -   7 Non-return valve    -   8 Duct    -   9 Reservoir    -   10 Pressure spring    -   11 Disk    -   12 Throughflow cross section    -   13 Valve body    -   14 Valve seat    -   15 Leakage gap    -   16 Non-return valve    -   17 Housing    -   18 Base    -   19 Flow cross section    -   20 Valve body    -   21 Valve seat    -   22 Flow cross section    -   23 Valve seat    -   24 Flow cross section    -   25 Valve seat    -   26 Flow cross section    -   27 Valve seat    -   28 Flow cross section    -   29 Valve seat    -   30 Gap dimension    -   31 Contact surface    -   32 a Section plane    -   32 b Section plane

1. A non-return valve of a hydraulic tensioning system of tractionmechanism drives of internal combustion engines, inserted between ahydraulic-fluid-filled pressure chamber and a reservoir, comprising: avalve body which is inserted in a housing and which is designed as aball and which, when the non-return valve is closed, is supported underspring loading against a valve seat of a throughflow cross-section,wherein, when the non-return valve is open, the valve body interactswith a valve seat of the housing, the associated flow cross-section ofwhich ensures a fluid flow through the non-return valve.
 2. Thenon-return valve as claimed in claim 1, wherein the valve seat, which ispositioned in a base of the housing, prevents the valve body from beingheld in a positively locking manner.
 3. The non-return valve as claimedin claim 1, wherein the flow cross-sections in a base of the housing areof any desired geometrical design.
 4. The non-return valve as claimed inclaim 3, wherein the flow cross-sections are of non-circular shape. 5.The non-return valve as claimed in claim 3, wherein the base of thehousing has at least an oval, multi-cornered or polygonal flowcross-section.
 6. The non-return valve as claimed in claim 1, wherein aplurality of bores is provided as a flow cross-section, with the valvebody influencing a fluid flow in all the bores.
 7. The non-return valveas claimed in claim 6, wherein the flow cross-section comprises threebores arranged close together.
 8. The non-return valve as claimed inclaim 2, wherein the flow cross-section is formed in a convexly shapedportion of the base, with a radius of curvature of the base differingfrom a radius of the valve body.
 9. The non-return valve as claimed inclaim 2, wherein the base is designed such that a contact surfaceassigned to the valve body form different curvatures with two mutuallyperpendicular section planes which each comprise one movement axis ofthe valve body.